1. Field of Invention
This invention relates to a material delivery/removal system for transporting grain, cement, and other dry stored materials from a storage bin, dome or other lateral enclosure. More specifically, the present invention relates to a bulk material delivery system for use with a free standing dome or shell-like storage bin.
2. Prior Art
Bulk storage of materials such as grain, cement, dry fuels and other commodities poses many problems which ultimately affect the availability of food, fuels and construction materials upon which each nation's economy depends. These problems range from storage requirements to special handling needs in material transport. The most difficult challenges typically arise when the bulk materials require both a controlled storage environment and unique handling profile during loading and unloading in storage areas.
Such materials include cement and similar bulk commodities which must be stored in a dry atmosphere. Because such materials require total enclosure for protection from the elements, convenient access for retrieval is typically limited. Although movable roofing permits direct use of scoop shovels and buckets to raise the bulk material to nearby trucks or rail cars, such facilities and methods are labor intensive and require a significant capital investment for equipment and special construction of buildings. As a consequence, industrial trends have focused on reducing the cost of storage and handling by simplifying construction of storage areas.
For example, free-standing dome structures have combined economical construction with the benefits of total enclosure. U.S. Pat. No. 3,456,818 illustrates a dome structure used for storing grains. Bulk materials are loaded within the dome through a top opening and are distributed outward by a rotating auger that drags the grain outward toward the laterally enclosing dome wall. This auger is designed to rotate along its longitudinal axis on top of the grain, as well as rotate radially around a center support post to provide redistribution of grain across the 360 degree top surface area of the grain. This dual rotation of the auger functions to maintain the auger in a "floating" configuration on top of the grain storage surface. The weight of the auger is carefully selected to enhance this floating performance as a necessary part of the system.
Outloading is accomplished by rotation of the center support post without the need for rotation of the auger about its longitudinal axis. An outlet port is formed in a floor surface below the support post and includes a subfloor auger which acts as a conveyer to transport material as it drops by gravity flow from the interior of the dome. Once the grain has reached its natural inclination of flow toward the central outlet port, the auger is activated to drag the remaining grain toward the center. Eventually, the total contents of the dome can be swept to the outlet port as the rotating auger cycles to a horizontal orientation near the floor surface.
Although the dome storage structure with transport system was invented approximately 25 years ago, it has experienced only limited commercial success. Its apparent limitation for use with bulk materials having physical properties similar to grains also inhibits its utility in other demanding storage needs such as with cement and other dry goods which are subject to greater compaction. These latter materials will naturally congeal to a rigid mass under the weight of the stored upper layers. This rigid mass is very difficult to break up and effectively blocks gravity flow of stored materials into the outlet. Because the auger assembly is designed to float on top of the grain, it has no significant influence on desired subsurface material movement.
In view of the numerous problems with the referenced dome storage system, access for movement of stored materials has generally been provided by lateral doors or openings at the base of the dome. These doors are opened and permit front-end loaders to use conventional loading techniques with scoop buckets or similar equipment to transport the materials. Unfortunately, highly compacted commodities such as cement do not readily collapse with removal of under support material. Indeed, a front-end loader may form a cavern opening of considerable size within the rigid base layer of material which could collapse without warning, causing potentially fatal results.
Such potential damage is not limited to just workers and equipment. It is well known that when a massive wall of caked material collapses within a silo or dome structure, the resultant lateral force impacting against a side dome wall could cause structural fracture. This results in loss of required structural integrity of the dome such that removal of the contained materials may also result in collapse of the total structure. In consequence of the risks associated with dome enclosures, common practice has tended toward more traditional storage construction such as silo bins, vertical wall enclosures, etc.
With respect to these traditional storage structures, a variety of inloading and outloading systems have been developed, including many utilizing an auger redistribution device. For example, U.S. Pat. No. 2,711,814 discloses an auger useful for cleaning flat bottoms of a grain tank. It operates in a manner similar to the auger system disclosed in the U.S. Pat. No. 3,456,818 above. Here again, this auger is designed for use with grain storage, and operates to substantially float on the top surface of the stored grain. Related auger transport devices have been used in silo storage systems, such as disclosed in U.S. Pat. No. 2,500,043; 3,755,918; 3,155,247 and 3,438,517. These patents are representative of a broad range of applications for the transport properties of an auger within a grain bin. Here again, these share the common feature that the auger device operates in a floating configuration at the top of the grain surface and transports materials in that configuration. The above cited patents demonstrate the common practice of placing the drive motor for the auger in a center mounted position, adjacent to a central support post or other central support structure. In most instances, this floating auger is cycled around a center axis, dragging particulate stored material toward the center of the silo for transport down a central tube or outlet to an underground conveyor.
Although the auger transport system has evidenced utility with respect to grains and other bulk materials, its principal application has been directed at surface movement of materials. Such applications suggest that such an auger system is not likely to be practical with respect to bulk materials which experience greater compaction, forming a rigid base layer. It is perhaps for this reason that much of the prior art technology utilizing an auger transport system is directed toward grains and other bulk materials which have less tendency to compact under pressure. The more flowable condition of these grains enables the outloading in conventional storage bins by mere gravity flow. The auger transport system functions primarily to redistribute bulk material toward the center of the storage bin to keep gravity flow in process throughout the outloading procedure.